In many scientific applications, it is necessary to distinguish the direction of passing neutrons. Traditionally, this has been a difficult thing to do inasmuch as neutrons are neutrally charged and therefore do not, by themselves, produce an electrical ionization in materials.
The prior art includes a number of detectors utilizing a converter layer of hydrogenous material, such as polyethylene adjacent to a silicon detector. When a neutron of sufficient energy passes through the hydrogenous layer, one or more protons will be liberated and the passage of these protons through the silicon layer results in the generation of a measurable electrical potential. However, these basic structures are only capable of detecting the presence of neutron flux, but are incapable of distinguishing the direction of this flux.
A recent concept proposed by Los Alamos National Laboratory incorporates a stacked structure of single alternating hydrogenous and silicon layers. The direction of incidence for a neutron can be deduced by measuring the track and total energy of a recoil proton as it passes through the detector. However, the concept requires a very highly segmented detector (e.g. microstrips) and copious signal processing as well as data analysis.
My previously mentioned co-pending application achieves directionality by unambiguously determining whether each neutron event is incident from the front or rear of the detector, with minimum signal processing and data analysis. In my prior invention hydrogenous layers are separated by stacked silicon particle detectors. An incident neutron passing through a first layer of hydrogenous material liberates a proton which then passes through the stacked particle silicon detector layers and deposits energy in each layer, the amount of which depends upon the thickness of a silicon layer and the proton-stopping power thereof. The signals produced by the silicon detectors are proportional to the energy loss in the detector layers and these will vary as the proton loses more and more energy during its travel through the silicon detector layers. Thus, a pattern of energy loss is established through the stack of silicon layers which, in turn, is indicative as to whether the neutron producing the recoil proton has entered the detector from a front direction or a rear direction. This determination may be made relatively simply and without the necessity of measuring the track and total energy of a recoil proton as it passes through the detector, as is the case with the most relevant prior art.
Although my prior invention operates satisfactorily, it relies upon the inclusion of more than three silicon detectors in each segment of a detector stack. This is a costly construction and adds to the size of a necessary unit. Also, the sensitivity or thresholding for my prior design required the switching of individual silicon detector layers from active to de-active states. This thresholding is therefore quantized in coarse, discrete levels.